Lean burn engines provide improved fuel efficiency by operating with an excess of oxygen, that is, a quantity of oxygen that is greater than the amount necessary for complete combustion of the available fuel. Such engines are said to run “lean” or on a “lean mixture.” However, this improved or increase in fuel economy, as opposed to non-lean burn combustion, is offset by undesired pollution emissions, specifically in the form of oxides of nitrogen (NOx).
One method used to reduce NOx emissions from lean burn internal combustion engines is known as selective catalytic reduction (SCR). SCR, when used, for example, to reduce NOx emissions from a diesel engine, involves injecting an atomized reagent into the exhaust stream of the engine in relation to one or more selected engine operational parameters, such as exhaust gas temperature, engine revolutions per minute (RPM) or engine load as measured by engine fuel flow, turbo boost pressure or exhaust NOx mass flow. The reagent/exhaust gas mixture is passed through a reactor containing a catalyst, such as, for example, activated carbon, or metals, such as platinum, vanadium or tungsten, which are capable of reducing the NOx concentration in the presence of the reagent. Typically, an injector is used for injecting the reagent into the exhaust stream of the engine.
An aqueous urea solution is known to be an effective reagent in SCR systems for diesel engines. However, use of such an aqueous urea solution involves many disadvantages. One of the disadvantages is the expansion of aqueous urea solution in frozen condition due to the formation of ice. Aqueous urea solution may tend to freeze in some situations, such as cold weather. Expansion of aqueous urea solution in frozen condition may damage one or more components of the injector. The injector may then have to be repaired or replaced, resulting in downtime and increased costs. Freezing of the reagent may also cause the injector to malfunction resulting in unwanted deposits in an exhaust system. Similarly, any other fluid delivery component may be damaged due to freezing of fluid.
Accordingly, it may be desirable to provide an improved reagent injector addressing some or all of these concerns.